Effects of Photoperiod on Growth, Digestive Enzyme Activity, Stress, and Oxidative Status of Juvenile Chinese Soft-Shelled Turtles (Pelodiscus sinensis) in a Greenhouse

Abstract

HIGHLIGHTSArtificial sunlight with the main components of UVB, UVA, and visible light was used to investigate the influence of photoperiod on large-scale farming of juvenile Chinese soft-shelled turtles in a greenhouse.The effects of photoperiod on digestive enzyme activity, stress, and oxidative status of juvenile Chinese soft-shelled turtles were revealed.The optimal photoperiod for juvenile Chinese soft-shelled turtles reared in a greenhouse was 0 h light:24 h dark.Abstract. To improve light conditions for soft-shelled turtles in a greenhouse, the effects of photoperiod on growth, digestive enzyme activity, stress, and oxidative status of juvenile Chinese soft-shelled turtles were investigated. In this study, juvenile Chinese soft-shelled turtles were reared under three photoperiods (hours light:hours dark), i.e., 0L:24D, 6L:18D, and 12L:12D) for four months. Results demonstrated that differences in growth were insignificant during the experiment, but the growth parameters of final weight, weight gain rate (WGR), and feed conversation ratio (FCR) were better at 0L:24D, and the survival rate was significantly higher at 0L:24D than at 12L:12D. Regarding digestive function, serum trypsin activity was significantly higher at 0L:24D than at 6L:18D, while lipase activity was significantly higher at 0L:24D than at 12L:12D. For the stress response parameters, serum cortisol level was significantly lower in turtles exposed to 0L:24D compared to the other treatments. With regard to antioxidant enzyme activities, the total antioxidant capacity (T-AOC) was significantly lower at 0L:24D compared to the other treatments, while superoxide dismutase (SOD) activity was significantly higher in turtles exposed to 0L:24D. The activity of glutathione peroxidase (GSH-PX) was significantly lower at 0L:24D than at 12L:12D. The malonaldehyde (MDA) activity was a little lower at 0L:24D than at 6L:18D; however, it significantly decreased in turtles exposed to 12L:12D. On the whole, the results indicated that the photoperiod treatments had no significant effects on the growth of juvenile Chinese soft-shelled turtles, while extended light exposure may cause physiological stress in turtles. Considering the survival rate, digestive function, cortisol level, and oxidative status, it is suggested that juvenile soft-shelled turtles should be reared under a 0L:24D photoperiod. Keywords: Chinese soft-shelled turtle, Digestive enzyme activity, Growth, Oxidative status, Photoperiod, Stress.